Tube Arrangement Research Articles

Air-Side Nusselt Numbers and Friction Factor’s Individual Correlations of Finned Heat Exchangers

Currently, when designing finned heat exchangers (FHE), the average value of the entire heat transfer coefficient (HTC) is considered. However, each row of the heat exchanger (HEX) has different hydraulic-thermal characteristics. The novelty of this research is to present the differentiation of the individual air-side Nusselt number and Darcy-Weisbach friction factor correlations in each row of FHE using CFD modelling. FHE has four-rows, circular tubes, and continuous fins with a staggered tube arrangement. Relationships for the Nusselt number and D-W friction factor derived for the entire exchanger based on CFD modelling were compared with those available in the literature, determined using experimental data. The maximum relative differences between the Nusselt number for a four-row FHE determined experimentally and by CFD modelling are in the range from 22% for a Reynolds number based on a tube outside diameter of 1000 to 30% for a Reynolds number of 13,000. The maximum relative differences between the D-W friction factor for a four-row FHE determined experimentally and by CFD modelling are in the range of 50% for a Reynolds number based on a tube outer diameter of 1000 to 10% for a Reynolds number of 13,000. The CFD modelling performed shows that in the range of Reynolds numbers based on hydraulic diameters from 150 to 1400, the Nusselt number for the first row in a four-row FHE is about 22% to 15% higher than the average Nusselt number for the entire exchanger. In the range of Reynolds number changes based on hydraulic diameter from 2800 to 6000, the Nusselt numbers on the first and second rows of tubes are close to each other. Correlations of Nusselt numbers and D-W friction factors derived for individual tube rows can be used in the design of plate-fin and tube heat exchangers used in equipment such as air-source heat pumps, automotive radiators, air-conditioning systems, and in air hot-liquid coolers. In particular, the correlations can be used to select the optimum number of tube rows in the exchanger.

Frozen curtain characteristics during excavation of submerged shallow tunnel using Freeze-Sealing Pipe-Roof method

The Freeze-Sealing Pipe-Roof (FSPR) method, which has been applied for the first time in the Gongbei Tunnel of the Hong Kong-Zhuhai-Macao Bridge, is a new approach of tunnel pre-support that allows flexible adjustment of freeze tube arrangement and can be adapted to different environmental conditions. When the FSPR method is used to construct shallow burial submerged tunnels, the frozen wall to hold back groundwater during excavation will be weakened by air and water flows inside and outside the tunnel, and its waterproof performance needs to be further investigated. In this paper, a two-dimensional numerical model of the temperature field considering excavation and moving water boundary is established based on the preliminary design scheme and in-situ conditions and is used to analyze the variation in frozen curtain properties with various active freezing times during excavation. The results show that excavation has a weakening effect on both sides of the frozen wall, with a greater effect on the inner side, and a positive temperature appears in the local area inside the jacked pipe. The concrete fill in the jacked pipe obviously improves the freezing efficiency, and the tunnel excavation after 60 days of active freezing in the interval filling mode can ensure that the frozen soil thickness at the thinnest segment exceeds 2 m, i.e., the design requirement. In practice, the active freezing time can be extended appropriately to reduce the influence of river water flow above the tunnel. The study serves as a technical reference for the design and implementation of similar projects.

Genetic Algorithm Integrated Fuzzy AHP-VIKOR Approach for the Investigation of W-Cut Insert Heat Exchanger for Cooling of Dielectric Fluid Used in Ultra-High Voltage Transformer

This study proposes a novel W-cut twisted tape to evaluate and enhance the effectiveness of novel grooved tube heat exchanger. The experimental investigations are carried out with W-cut inserts, which possess two main control factors, namely, twist tape ratio (y = 3.5 to 6.5) and width tape ratio (WR = 0.43 to 0.6). The investigation results prove that in all cases the energy transmission and friction factor of W-cut insert along with the first law and second law efficiency are considerably higher than the conventional tube arrangement. The empirical model equations for friction factor, performance enhancement ratio, Nusselt number, and rational efficiency are developed, and they show good affinity with experimental data. Since the abovementioned factors have conflicting terms, it is essential to select the proper operating configuration of the heat exchanger in order to increase the thermal energy transfer rate with reduced consumption of pumping energy. The multi-objective genetic algorithm (GA) tool is used to identify the optimum operating conditions. Further, the hybrid multi-criteria decision-making model, FAHP-VIKOR, is applied to select the perfect model from the set of non-dominated solution. The ranking of alternatives is as follows: A4 > A11 > A2 > A9 > A21 > A17 > A1 > A24 > A11 > A23 > A7 > A18 > A13 > A10 > A20 > A5 > A19 > A14 > A16 > A22 > A25 > A6 > A15 > A3 > A8. The optimized configuration of W-cut insert is compared with the former inserts, and the optimal configuration exhibits supreme performance than other inserts.

Numerical investigation on heat transfer and pressure drop characteristics of moisture separator reheater with porous media method

The geometry structure of the Moisture separator reheater is very complex, which makes it almost impossible to calculate the whole domain and analyze the physical characteristics. To get the three-dimensional physical property distribution of the moisture separator reheaters, the porous media method is used to simplify the geometry. The 1-dimensional and 3-dimensional coupling theory is adopted into the calculation, for the primary side inside the finned tubes is iterated as the one-dimensional distribution, and the secondary side outside the finned tubes are treated as three dimensional. The whole process of conducting the porous media methods is illustrated with the value. Both the calculated and experimental results of the pressure drop are about 10 kPa in the 1st and 2nd reheaters. The calculation results provide a design and safety evaluation of the moisture separator reheater, as the three-dimensional physical distribution is got through the porous media calculation. With different input parameters such like the arrangement of the finned tubes, the calculated results of heat transfer and pressure drop will be different, and the calculated results are helpful to the design and optimization of the finned tube reheaters. This will help design a set of finned tube parameters.

Steam Methane Reforming with Chemical-Looping Combustion: Scaling of Fluidized-Bed-Heated Reformer Tubes

The combination of chemical-looping combustion (CLC) and steam methane reforming (SMR) bears the potential for quantitative and energy-efficient CO2 capture along with hydrogen production from natural gas. A 2-dimensional axisymmetric model of a SMR tube was used to estimate the possibility to adapt the tube dimensions to better fit into fluidized-bed heat exchangers. A constant surrounding fluidized-bed temperature was set as the boundary condition. There are two phenomena that affect the reactor performance: the effective heat-transfer rate from the fluidized bed to and through the tube wall and onward to and into the catalyst bed on the one hand and the effective reaction rates of the governing chemical reactions on the other hand. Literature models were used for the heat-transfer description assuming a state-of-the-art reforming catalyst and classical SMR kinetics were formulated. The simulation results show a temperature decrease toward the tube center in steady state operation. The gas phase composition at the tube outlet reflects the radial temperature distribution as the chemical equilibrium is approached well. Simulations with smaller tube diameters indicate that the necessary tube length for equivalent gas conversion is significantly reduced. In a 1/2-scale setting with 63 mm inner diameter (ID) of the tube instead of 126 mm ID in full scale, the necessary tube length is only 6.0 m instead of 12.5 m, and in a 1/4-scale setting with 31.5 mm ID, the necessary tube length is only 3.3 m. A temperature increase of the fluidized bed from 900 to 950 and 1000 °C may reduce the necessary tube length in the 1/4 scale from 3.3 to 2.6 and 2.2 m, respectively. These indications are promising with respect to the possibilities for fluidized-bed immersed reformer tube dimensioning and arrangement. More detailed reactor design studies will be necessary to judge the industrial feasibility of the CLC-SMR combination.

Numerical modeling based machine learning approach for the optimization of falling - film evaporator in thermal desalination application

Scale formation that drastically increases thermal resistance and reduces freshwater production remains a critical challenge in thermal desalination. Novel designs of falling film evaporator and optimal operating condition hold great promise to mitigate scale formation, and increase heat transfer performance and fresh water production. In this work, CFD simulation based machine learning and multi-objective optimization are performed to identify optimal conditions and tube arrangement for evaporator. Non-dominated sorting genetic algorithm is adopted to determine and analyze the optimal pareto front for multiple objectives in desalination criteria. The errors of training, validation, and testing set are computed to identify an optimal hyperparameter set. For performance ratio, fouling resistance, and water production rate, the average relative error is 2.26%, 3.67%, and 3.24%. At pareto front, both performance ratio and water production rate increase at high temperature with fouling resistance (thermal resistance of the fouling layer) increasing as well. Tradeoffs between mitigating scale formation and enhancing desalination performance are evaluated in optimizations for different objectives. Potential optima are identified and can be applied as guidelines to determine evaporator design and system operating conditions.

Experimental investigation on the impact of tube bundle designs on heat transfer coefficient in gas-solid fluidized bed reactor for Fischer-Tropsch synthesis

The impact of vertical heat exchanging tube bundle on heat transfer coefficient (HTC) has been investigated locally and instantaneously using a sophisticate heat transfer technique using glass beads solid particles of 210 μm average size and 2500 kg/m3 solid density (Geldart B particles), with a static bed height of 0.35 m as bed material. A mimicked Fischer-Tropsch fluidized bed with vertical heat exchanging tubes is designed and built in this study. Heat transfer performance is also investigated by using two different tubes arrangement (square-pitch and triangular-pitch tubes arrangement). To represent the heat exchanging tubes used in the Fischer–Tropsch process, stainless-steel heat exchanging tubes inserted vertically, each with a diameter of 0.012 m, were used in each tubes arrangement occupying 25% of the column cross-section area. The experiments were performed in a 0.13 m inner diameter Plexiglas fluidized bed reactor with varied gas flowrates (0.2–0.48) m/s at numerous radial positions along the diameter of the column (±0.58, ±0.33, and ± 0.03) and two axial locations (H/D = 1.153 and 1.923). It was found that HTCs significantly enhance with increasing the gas flowrates for all radial positions for square-pitch tubes arrangement. While different behavior can be noticed in the radial positions with triangular-pitch tube arrangement, especially near the wall region (±0.33). Also, the local heat transfer coefficient (LHTC) improved with increasing the axial positions by 12.06% at highest gas flowrates (0.48 m/s). Moreover, the square-pitch tubes arrangement showed a significant increase and uniformity in HTC when measured instantaneously comparing with other tubes arrangement. Furthermore, the findings of this study will improve awareness of vertical tubes' effect on heat transfer in a fluidized bed reactor. Moreover, the data acquired from this investigation can be employed to validate reactor models, CFD codes, and simulations in order to support the design and scale-up processes of such reactors.

Numerical investigation on melting and energy storage density enhancement of phase change material in a horizontal cylindrical container

Thermal energy storage (TES) plays a significant role in storing heat energy during the availability of a source. The phase change material (PCM) storage density is high, but its meager thermal conductivity leads to ineffective heat transfer. This mathematical modeling work simulates two different heat transfer tube (HTT) arrangements in a horizontal cylindrical container to melt the PCM using the enthalpy-porosity method. Case-1 with a single HTT at the centroidal axis and Case-2 with multiple tubes spread radially. Cases-1 and 2 are observed with melting and solidification duration of 39.8 and 184 minutes, and 69.83 and 292.5 minutes respectively. Case-1 has a shorter melting and solidification time because of the optimal HTT location. Case-2 is observed with a high heat storage density of 224.95 MJ/m3, compared to Case-1 with 224.571 MJ/m3. Nusselt number is higher for Case-2 (385.86) during charging and higher for Case-1 (208) during discharging. Nusselt number initially varies for both cases due to effective heat convection at the start; however, Case-1 has a shorter melting duration with its energy density lower than the Case-2. Based on the obtained results, it could be suggested that Case-1 could be applicable when simultaneous heat transfer requires less energy storage and a faster melting rate, while Case-2 could be used in places that demand a higher storage density.

CFD ANALYSIS FOR HEAT TRANSFER AND PRESSURE DROP IN TUBE BUNDLE OF CROSS-FLOW HEAT EXCHANGER

In the present work, the preliminary finding of possibilities of heat transfer and pressure drop is reported across the shell and tube arrangement cross-flow heat exchanger. The heat exchanger consists of cold-water flows through the bundle of circular tubes and hot air across the shell. Like in the conventional arrangement, the flow in adjacent rows of tubes is normal to the fluid flow in the shell in the cross-flow arrangement. The three-dimensional turbulent flow region is modelled by employing ANSYS FLUENT 21.0. The standard k-ε model is used to model the turbulence flow. A SIMPLE algorithm scheme is applied to link the pressure and velocity fields inside the domain for air fluids. The heat transfer in the water inside the tubes is represented by a convective boundary condition. The tube flow Reynolds number was fixed at 2200 and the shell flow Reynolds number was varied from 6000 to 10000 in the turbulent zone. The purpose of this paper is to determine temperature reduction and pressure drop across the tube bundle. The simulation will predict the temperature of the airstream at the heat exchanger exit and the pressure drop. The results indicated that there is a significant amount of temperature drop in the air that releases the heat due to forced convection and temperature drop continues in the turbulent region of the incoming fluid.

Fluidelastic instability research of tube bundles by a two-way fluid-structure interaction simulation

Fluidelastic instability (FEI) could cause serious damage to the tube bundle, and streamwise FEI has attracted more attention in recent years. Water tunnel experiments have been conducted to investigate streamwise and transverse FEI in a parallel triangular tube bundle with a single elastic tube in center. RMS displacement-reduced velocity relationship diagram, vibration time-history curve and frequency spectrum response in streamwise and transverse directions are obtained. A Two-way fluid-structure simulation method was developed to calculate the streamwise and transverse FEI. The motion of the elastic tube was controlled by a User-Defined Function (UDF) coupled with dynamic mesh. The FEI tendency of simulation is consistent with experiment results but the values of predicted critical reduced velocities are more conservative. The process of FEI was analyzed. Finally, the model was extended to explore the effect of pitch diameter ratio, elastic tube arrangement and natural frequency ratio of streamwise and transverse.

Experimental study of drilling riser and wellhead force by small scale testing

Small-scale model tests of a drilling riser were conducted, aiming at a better understanding of the mechanical transfer of forces from the drilling riser to the wellhead. The tests were conducted in a water tank with wave-making and flow-making functions, and strain gauges were installed along the riser model to estimate the riser curvature and stresses imposed on the wellhead. This paper discusses the effects of the environmental conditions, the platform offset, the dimensions of the riser and position of the buoyancy tube on the riser response and the stresses transferred to the wellhead. Obviously, the results indicate that increasing the riser dimensions, at more harsh environmental conditions, and increasing platform offsets will increase the stress at the wellhead. Among the four buoyancy tube arrangements (staggered, top, middle, and bottom arrangements), the staggered arrangement leads to the smallest wellhead stresses, whereas the wellhead stresses for the other three arrangements are also very close. The results of the small-scale experiments are found to be consistent with the results based on numerical calculations. By considering the results from the numerical simulations and full-scale experiments reported in the literature, the results of the present study are found to both confirm and extend the accumulated knowledge based on those studies.

Study of the Impact of Tube Configurations on the Local Heat Transfer Coefficient in Mimicked Fischer-Tropsch Bubble Column Reactor

An experimental investigation was conducted to examine, for the first time, the influences of using different designs of tube arrangements on the local heat transfer coefficient (LHTC) in a bubble column (with a diameter of 0.13 m) equipped densely with a bundle of tubes. The effect of using two different designs of tube arrangements has been examined for a broad range of gas flow rates using a sophisticated heat transfer technique. The obtained results indicate that the LHTC increases significantly with increasing the gas velocity, regardless of the design and installation of the tubes in the column. Additionally, the shape of the LHTC’s profiles alters considerably by the presence of a bundle of tubes and their arrangements. Moreover, the results indicate that the square tube pitch arrangement provides uniform heat transfer profiles, which enhance the performance of the bubble column reactor by 30%. Furthermore, the heat transfer profiles were found to be varied with the axial height of the column. The new experimental results obtained in this investigation will provide experimental reference data for creating and validating a mathematical model for predicting LHTCs. In addition, this will facilitate this kind of reactor’s design, scale-up, and operation.

Study on thermal performances of a horizontal ground heat exchanger geothermal system with different configurations and arrangements

Horizontal ground heat exchanger (HGHE) is a low-cost shallow geothermal exploitation method compared with vertical ones, but it needs more land area. Optimizing geometrical configurations and arrangements of ground heat exchangers is desirable to enhance heat exchange per unit land area. However, a comprehensive study on different HGHE configurations and arrangements considering atmosphere-soil-HGHE interaction is still inadequate. To this end, thermal performances of four configurations, including slinky, spiral, multi-tube with serial connection and tiled tubes, are compared based on a 3D numerical model for HGHE considering atmosphere conditions variation and humidity migration. Effects of main geometrical parameters on HGHE performance and economical efficiency are investigated for these four configurations. Finally, different tube arrangements of multi-tube HGHE are designed and their thermal performances are analyzed. Results indicated that longer HGHE tube length has better thermal performance but lower economical efficiency, thus being not advisable for the HGHE design. Among these four configurations, multi-tube with serial connection shows the best thermal performance. Increasing the tube spacing is beneficial for reducing the tube mutual interference and enhance the heat exchange per unit land area, which is recommendable. Results are expected to provide meaningful suggestions for the HGHE design.

Experimental investigation of heat transfer from elliptic tubes heat exchanger immersed in a fluidized bed

In this work, heat transfer, wall-to-bed, characteristics from elliptic tubes heat exchangers, both inline and staggered tubes arrangements, were studied experimentally. Bundles of twenty tubes of the same total surface area of 0.015 m2 and a length of 200 mm are immersed in a bed of granulated charcoal of different grain sizes, 2, 4 and 6 mm. Air was used as a fluidizing fluid. One of these tubes which was made of copper, instrumented, electrically heated and positioned in the middle of tube bundle, while the others are wooden dummy to be influenced only by the presence of the neighbouring tubes. Measurements are reported in the range of fluidization number within range of 1 to1.4. The results showed that, the local Nusselt number around the elliptic heated tube is about uniform with its maximum value at the tube sides and minimum at the stagnation and rear points of the tube. In addition, the average Nusselt number increases with the increase of the fluidization number and with the decrease in particle diameter. Heat transfer characteristics were found to improve in staggered tube bundle if compared with the inline tube arrangements. The present results of pressure drop and average Nusselt numbers were validated with a numerical model of the same conditions for the case of particle diameter of 2 mm. Good qualitative and quantitative agreements have been achieved between experimental and numerical data. Finally, correlation equations for the average heat transfer in terms of Nu, fluidization number and tube to particle diameter ratio are deduced.

Studi Eksperimen Kinerja Penukar Kalor Kompak Sebagai Pemanas Tambahan di Rumah Pengering Hibrid

The process of drying a hybrid system that uses a combination of solar energy and biomass contains some useful heat in the chimney of the biomass stove. This heat waste has a high enough temperature so that with the help of a compact heat exchanger it can be used as an additional heater. The purpose of this study was to analyze the performance of a cross-flow type discrete flat plate-finned tube compact heat exchanger with an inline tube arrangement which is used as an additional heating device in the hybrid dryer housing. The test was carried out at 10.00-15.00 for three days of testing with variations in air flow velocity of 1.3 m/s, 1.6 m/s and 1.8 m/s while the velocity of water flow in the pipe was considered constant with 0.000168 m/s. s and the air flow velocity in the exhaust fan is kept constant at 1 m/s. The results of this study indicate that the overall heat transfer coefficient is strongly influenced by the effectiveness of the heat exchanger, and with the increase in the effectiveness of the heat exchanger, the heat transfer coefficient will also increase. The highest overall heat transfer coefficient was obtained on the second day, namely 99.263 W/m2.oC. The total heat transfer rate is influenced by the effectiveness of the heat exchanger but at a certain value both values ​​tend to be stable due to the limited dimensions of the heat exchanger. NTU is very influential on the effectiveness of the exchanger, and in this case the value of NTU ranges from 0.6-0.8 while the effectiveness of the heat exchanger ranges from 46%-56%

Heat transfer enhancement of supercritical CO2 in solar tower receiver by the field synergy principle

The supercritical CO2 used as heat transfer fluid (HTF) in solar tower cavity receiver has higher pressure and operating temperature, and lower investment than traditional heat transfer fluid, such as water steam, molten salt, etc. Many researchers have analyzed the effects of mass flow rate, heat flux, tube diameter, operating pressure and inlet temperature near the critical point on the heat transfer performance of supercritical CO2. However, there are few studies on the convective heat transfer characteristics of supercritical CO2 in tower solar receivers under the non-uniform heat flux boundary. In this contribution, in order to improve the convective heat transfer performance of supercritical CO2 under non-uniform heat flux, we firstly analyze the effect of the arrangement of the receiver tube on the flow and heat transfer performance of supercritical CO2. Then, we apply the field synergy principle to guide the flow field enhancement, and design the non-uniform structure at the position with larger field synergy angle. Finally, we further analyze the effect of the non-uniform structure on the heat transfer performance of supercritical CO2. The results show that the triangular ribs tube is the best heat transfer enhancement structure, e.g., when the mass flow rate is 0.1 kg·s−1, the Nusselt number is 956.11, which is 163% higher than that of the smooth tube. This contribution can provide a guidance for the structural enhancement of a practical supercritical CO2 solar receiver to improve the heat transfer performance.

Experimental validation of a continuum model for local heat transfer in shell-and-tube moving-bed heat exchangers

• Local heat transfer coefficients in shell-and-tube moving bed heat exchangers were simulated. • Local heat transfer coefficients were measured using a small heat exchanger mockup. • Experimental results were used to validate a comprehensive thermal model. • Simulation results were in good agreement with the experiments. Moving-bed heat exchangers with a horizontal tube arrangement offer a promising solution to exchange high-temperature heat with a particle stream. However, in order to guide the design of such heat exchangers, accurate and time-efficient simulation tools capable of capturing the complex heat transfer characteristics still need to be improved. In this article we present experimental results of the local heat transfer coefficients around the tube circumference of a heat exchanger mockup. To this end, specially prepared measuring probes were developed and a test campaign was conducted. A comprehensive thermal model was applied to the setup under consideration. This model takes into account the temperature-dependent thermophysical properties of the bulk, variable temperature boundary conditions, and the increased thermal resistance caused by the stagnation and void zones. To validate the model, calculated and experimental results were compared. It turns out that the predicted heat transfer coefficients well match the experimental data, albeit with slight deviations at the stagnation and void zones of the tubes. The prediction of a tube’s area-weighted heat transfer coefficient, which constitutes the most important factor for design purposes, yields results with errors of less than 3%. Therefore, it is concluded that the proposed thermal model is able to well predicts the heat transfer in shell-and-tube moving-bed heat exchangers.

Experimental investigation on multi-layered filament wound basalt/E-glass hybrid fiber composite tubes

In this study, the mechanical damage of Basalt/E-glass hybrid fiber-reinforced polymer composite tubes was evaluated experimentally using Micro hardness on transverse direction, uni-directional static tensile loading, and Quasi-static compressive loading. The Burn-off test method has been studied for the volumetric fraction of hybrid composite tubes. The multi-layer hybrid composite tubes composed of eight layers of plies at constant fiber tension of 20N, a constant mandrel rotation speed of 45 RPM and constant winding angle of ±55° for basalt fiber and ±90° for E-glass fiber were fabricated through a 3-axis filament winding machine with a seamless amalgamation of the stage by stage curing in the furnace. Eleven tube arrangements with fiber content proportion of {100%, 25:75%, 50:50% and 75:25%} with various stacking sequence were studied. The test results provide that these mechanical property’s behavior was moderately affected by the proportion of fiber content and most of the time affected by the variation of layer stacking sequence. Adding 50% of basalt and 50% E-glass fiber sharing of BGH7 hybrid combination of basalt laminate placed in the outer side increases the mechanical characterization compared to the 25% and 75% sharing of basalt and E-glass fiber. The fractured fibrous matrix of the tensile specimens and compressive specimens was assessed using a scanning electron microscope (SEM).

Experimental investigation of heat transfer enhancement and pressure drop of fin-and-circular tube heat exchangers with modified rectangular winglet vortex generator

The presence of vortices in a flow field significantly impacts heat transmission. The effect of a modified rectangular winglet vortex generator on heat transfer and pressure drop performance for a fin-tube heat exchanger (FTHE) is experimentally explored in this work. Design and fabrication of full-scale prototype of an FTHE are carried out. Two types of rectangular winglet vortex generators (RWVGs), i.e., Flat RWVG and RWVG with a circular punched hole are installed into the FTHE for experimentation purposes. The experimental studies are conducted with Reynolds numbers ranging from 8000 to 25,000. The experimental results show that the use of RWVG in FTHE provided a much greater heat transfer coefficient than FTHE without RWVGs with an increase in pressure loss penalty. For better wake management, the RWVG are installed behind the circular tubes in a common flow down (CFD) arrangement. The comparative study is carried out to explore thermo-fluid performance of fin-and-tube heat exchanger with two inline circular tube arrangements for all considered cases of RWVGs. By varying the tube wall temperature (i.e., 65, 75, and 85 °C), thermo-hydraulic performance criteria such as Nusselt number (Nu), friction factor (f), and thermal performance factor (η) are compared. Lower tube surface temperature gave the highest enhancement in heat transfer performance with a lower friction factor. However, the thermal performance factor (η) for the RWVG with a circular punched hole is about 1.04–3.2%, 1.3–5.4% and 2.3–10.52% higher than RWVG-Flat for the tube wall temperature 65 °C, 75 °C, and 85 °C, respectively.

Numerical investigation on the thermal-hydraulic performance of separated structure steam generator with different tube arrangements

The horizontal steam generator is generally used in nuclear power plant and industry to produce steam. To increase the heat load and reduce the size, a steam drum can be added above the shell. However, it makes the overall flow of water cycle complicated. In this article, the two-phase boiling flow and heat transfer inside tube bundle under the separated structure has been investigated numerically based on the previous experiment. The Drift-Flux model was utilized to solve the equations of heat and mass transfer in the mixture flow. The local pressure drop, void fraction and heat transfer characteristics have been presented and discussed for different arrangements in detail. The analysis results showed that the overall boiling HTC of the tube arrangements of 30°and 60° appear better for this steam generator under the same condition. The boiling heat transfer in both bottom and upper tube bundle was mainly controlled by the nucleate boiling mechanism. However, both heat flux and vapor void fraction were found to affect the heat transfer performance. Beyond this analysis, a new type of heat transfer correlation has been proposed herein to evaluate the local HTC with a good accuracy. These correlations allow better predictions of the boiling heat transfer inside the SS-SG, which provide designers with better reference and guidance.